Certain cigarette making machines, such as the Molins Mk8 and Mk9 models, include means for forming a continuous tobacco rod from tobacco filler material and from a continuous length of cigarette paper having a width equal to slightly more than the circumference of the cigarette rod. The cigarette paper is fed onto a moving flexible garniture belt and the tobacco filler is deposited onto the paper. The garniture belt, cigarette paper and filler resting thereon are then formed into a rod shape as they are passed between a tapered concave up garniture positioned below and acting on the lower surface of the belt and an opposed tapered concave down tongue (also referred to in the art as the "short" tongue) positioned above and acting on the filler. As the rod leaves the tongue-garniture area, the edges of the paper are brought together in an overlapping fashion to encompass the filler material. The overlapped edges are adhered, thus completing the formation of the continuous tobacco rod. Downstream, the rod is cut into lengths to form a filterless cigarette. A filter may be added if desired.
To ensure that a desirable firmness of the tobacco rod is obtained, some cigarette making machines incorporate a sensor to detect such firmness. The firmness may be adjusted in response to the sensed firmness by regulating the amount of tobacco filler fed onto the paper.
One such sensor design is shown in Nienow, et al., U.S. Pat. No. 4,033,360, July 5, 1977. The Nienow device provides a strain gauge arrangement fitted on an arm supporting the tongue. As tobacco moves through the garniture area of the cigarette maker, the tobacco is compressed between the garniture and the tongue. The tongue and the arm supporting the tongue are deflected by the compressed tobacco. The degree of deflection corresponds to the rate of tobacco feed and to the resulting tobacco rod firmness. The signal generated by the arrangement is proportional to the degree of deflection and this is indicative of rod firmness. The signal may be calibrated by incrementally regulating the tobacco feed rate to make tobacco rods having a range of firmnesses while noting the corresponding signal value. The firmness of the rods so formed may be accurately measured in the laboratory to establish the signal-firmness correlation.
Another design is shown in Strydom, U.S. Pat. No. 4,010,762, Mar. 8, 1977, wherein the tongue is separated into two portions, the downstream portion being connected by an arm to the upstream portion and a strain gauge being mounted on the arm. As in Nienow, the signal generated by the strain gauge is indicative of rod firmness. A second Strydom arrangement utilizes a segment disposed in an aperture in the concave garniture below the garniture tape. The segment is mounted on an arm having a strain gauge attached thereto.
These prior arrangements suffer the problem of losing the calibration of the strain gauge. This problem is the result of dimensional changes in and between the tongue and garniture. These changes may sometimes arise because the mounting may shift due to vibration or the like. However, more often, these changes arise because positional adjustment of the tongue piece is periodically required to compensate for dimensional changes resulting from the wearing away of the surface of the tongue piece by the tobacco rod components passing thereover and the wearing away of the thickness of the garniture belt from rubbing against the garniture. Wear is particularly severe at the downstream tip of the tongue piece. When the position of the tongue piece is adjusted, the calibration of the strain gauge apparatus must also be redetermined.
This is also true for the second mentioned Strydom arrangement because the segment acts against the tongue through the garniture tape, paper and filler. Moreover, this segment arrangement of Strydom suffers from the additional disadvantage that the firmness properties of the garniture belt, against which the segment acts, directly influence the sensor indication. Thus, any change in such properties caused by belt wear or flexure during belt life directly affects the sensor reading and results in erroneous readings.
Accordingly, there is a need in the art for a sensor arrangement, strain gauge, or otherwise, that does not require adjusting when the tongue is adjusted.